Mekong Delta

• Category: Inland Aquatic Biomes.
• Geographic Location: Asia.
• Summary: The richly diverse habitats of the vast Mekong Delta, heavily affected by past exploitation and destructive events, are newly threatened by rapid and uncontrolled development.

The Mekong Delta, the final downstream portion of one of the longest rivers of the world, extends to the southern tip of Vietnam and Cambodia on a triangular plain of approximately 21,236 square miles (approximately 55,000 square kilometers). It is the third-largest deltaic plain in the world, after the Amazon River delta and that of the Ganges-Brahmaputra system. The delta includes a wide variety of ecosystems. It faces several key environmental problems, mainly related to largely unsustainable economic activities and to its historical background.

The Mekong River flows for more than 2,485 miles (4,000 kilometers) from the Tibetan plateau to the South China Sea, crossing six countries: China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. The collision of the Indian tectonic plate with the Eurasian continent resulted in tectonic uplift and folding, which in this area shaped a variety of physical landscapes, ranging from mountains and highland in the northern regions, to broad floodplains in the southern ones.

In the vicinity of Phnom Penh in Cambodia, the main channel of the river divides into two distributaries: the Mekong and Bassac rivers, considered to be the northern extremity of the deltaic system. The water network subsequently splits into nine main channels, giving this area the name Nine Dragons River Delta. The triangular delta extends from Phnom Penh in the northwest to the southern Vietnamese province of Soc Trang in the southwest and to the mouth of the Saigon River in the east.

The delta is characterized by a complex hydrographic network that includes about 5,592 miles (9,000 kilometers) of large and small channels. The Gulf of Thailand and the South China Sea, characterized by different tidal regimes, affect the duration of flooding and the salinity of the brackish waters and soils. This hydrographic complexity determines the presence of different soil types that influence the associated ecosystems.

According to topography, properties of the sediment, and agro-ecology, researcher Nguyen Huu Chiem divided the delta into five different land-form units: floodplains, a coastal intertidal complex, a broad depression, old alluvial terraces, and the hills-and-mountains district.

Biodiversity

Plants found in the Mekong Delta area tend to be types that thrive in the tropical moist, swampy environment. Tree communities are important to maintain the health of the ecosystem; for example, they prevent water runoff during the rainy season. Reed beds form important habitats here for waterfowl, including the eastern sarus crane (Grus antigone) and various ibis, such as the near-endemic Pseudibis gigantea, or giant ibis. Mammals commonly found in the area include such ungulates as Eld’s deer (Rucervus eldii siamensis) and the Indochinese hog deer (Axis porcinus annamiticus).

The main river of the Mekong holds three times more fish species per unit area than the Amazon River. The Mekong giant catfish (Pangasianodon gigas) makes its home here. This large, almost mythical fish, can reach up to just under three meters. The species is critically endangered due to overfishing and habitat loss. Also found in the river are the short-clawed otter and the Irrawaddy dolphin.

Threats

The two Indochina wars in the second half of the 20th century deeply affected both the social and the environmental frameworks. During the second war, largely known as the Vietnam War (1955–75), 20 million gallons (75 million liters) of toxic herbicides and defoliants such as the notorious Agent Orange were sprayed on large areas of the delta, targeting both forested areas and agricultural lands.

All the mangrove forests in the Dong Nai river system and 40 percent of the mangrove forests in the southern part of the delta were destroyed. About 3 million people were affected by the toxic chemicals, and a massive migration from rural to urban areas affected the whole socioeconomic structure of this region.

In spite of the dramatic human loss that occurred in this period, the population in the delta increased by one order of magnitude, from 1.7 million people at the end of the 19th century to nearly 17 million people today. This growth has driven intensive development of primary agricultural activities, which in this region are constituted mainly of rice production and aquaculture.

After the end of the Vietnam War, an explosive expansion of the network of canals strongly affected the delta ecosystems in new ways, even as they provided access to previously undisturbed extensive wetland portions. Surface and subsurface waters were drained, decreasing the average period of flooding from year round to four to six months per year. The resulting dramatic changes in ecological conditions had widespread negative effects, such as soil acidification, saline intrusion, and pesticide pollution. In many cases, the exploitation of acid sulphate soils failed, with both socioeconomic and environmental fallouts: The number of landless farmers increased, and the original forests could not recover, leading to overall decline in biological diversity.

The fisheries industry in the delta is based on aquaculture farms that raise several species of shrimp and prawn (e.g., Penaeus, especially P. monodon) and fish (Pangasius bocourti and P. hypophthalmus).

Currently, shrimp aquaculture is considered to be the single most important factor responsible for the destruction of mangrove forests in the Mekong Delta, although these forests reportedly play a fundamental role in the maintenance of shrimp productivity. Despite some attempts at sustainable management, such as integrated mangrove-silviculture-prawn-aquaculture systems, most shrimp farming activities are conducted in an unsustainable way, with producers such as multinational companies rapidly exploiting local areas and moving to others, clear-cutting the mangrove forests and installing shrimp ponds. However, a 13,591-acre (5,500-hectare) aquaculture project in the Mekong Delta is expected to increase the overall production of all seafood. The $26.6-million project will provide infrastructure such as irrigation, roads, and power supply systems. When completed in 2026, it is expected to annually produce 534,401 tons (484,800 tonnes) of seafood.

Development projects that threaten the natural ecosystems of the delta range from the elimination of periodic flooding by damming and building upstream reservoirs, and diking river banks to the rapid increase of industrial activities, deeply affecting the hydrological regime and sedimentation rates. Recently, a damming project in the upper part of the Mekong River, part of the Xayaburi Dam in Laos, has been the object of debates between the Laotian government and the Mekong River Commission about possible consequences on the Mekong fisheries, including the migratory Mekong giant catfish and the river’s giant freshwater stingray (Dasyatis laosensis).

Climate change is another significant threat to the region. Experts note that rising sea levels are causing the delta land form to quickly recede. They predict that by 2100, most of it will be below sea level, displacing approximately 17 milllion people.

Conservation Efforts

To cope with the rapid and deep alterations of the environment, several management and conservation measures have been taken. Six reserves have been established to protect parts of the wetland ecosystems of the delta, for a total area of about 77 square miles (200 square kilometers). In 1983, a joint research unit of the Mekong River Commission and the United Nations Environment Programme (UNEP) developed ecologically compatible measures to be adopted in the exploitation of water and land resources.

In 1986, Vietnam and Cambodia signed an international agreement on cooperation in wildlife conservation, attaching special importance to endangered waterfowl species, which are particularly abundant in this area. In a more recent review, 16 organizations, programs, and networks focused on the conservation of the Mekong River basin. Despite these attempts, sustainable approaches to better management of the economic activities of the area are considered to remain urgent priorities—and complex challenges.

Bibliography

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Chiem, Nguyen Huu. “Geo-Pedological Study of the Mekong Delta.” Southeast Asian Studies 31, no. 2 (1993).

Christensen, S. M., D. J. Macintosh, and N. T. Phuong. “Pond Production of the Mud Crabs Scylla paramamosain (Estampador) and S. olivacea (Herbst) in the Mekong Delta, Vietnam, Using Two Different Supplementary Diets.” Aquaculture Research 35, no. 2 (2004).

Ellison, Aaron M. “Managing Mangroves with Benthic Biodiversity in Mind: Moving Beyond Roving Banditry.” Journal of Sea Research 59, nos. 1–2 (2008).

Kondolf, G.M., et.al. "Save the Mekong Delta from Drowning." Science, vol. 376, no. 6593, pp. 583-85, 5 May 2022, doi.org/10.1126/science.abm5176. Accessed 20 Nov. 2024.

"Mekong Delta Lands $26 Million Aquaculture Investment." Global Shrimp Forum 2022, 26 July 2022, thefishsite.com/articles/mekong-delta-lands-26-million-aquaculture-investment. Accessed 20 Nov. 2024.

Stewart, Mart A., and Peter A. Coclanis. Environmental Change and Agricultural Sustainability in the Mekong Delta. New York: Springer, 2011.

Tong, Phuoc Hoang Son, et al. “Assessment From Space of Mangroves Evolution in the Mekong Delta, in Relation with Extensive Shrimp-Farming.” International Journal of Remote Sensing 25, no. 21 (2004).

Torrell, Magnus, Albert M. Salamanca, and Blake D. Ratner. Wetlands Management in Vietnam: Issues and Perspectives. Penang, Malaysia: World Fish Center, 2003.

“Wetlands of the World: Mekong Delta- Vietnam and Cambodia.” Wildfowl and Wetlands Trust, 21 Jan. 2021, www.wwt.org.uk/news-and-stories/blog/wetlands-of-the-world-mekong-delta-vietnam-and-cambodia/#:~:text=The%20Mekong's%20main%20river%20holds,change%20on%20the%20poorest%20communities. Accessed 20 Nov. 2024.